In energy-assisted magnetic recording (EAMR), the recording medium is locally heated to decrease the coercivity of the magnetic material during write operations. The local area is then rapidly cooled to retain the written information. This allows for magnetic write heads to be used with high coercivity magnetic materials. The heating of a local area may be accomplished by, for example, a heat or thermal source such as a laser. As such, one type of energy-assisted magnetic recording is heat assisted magnetic recording (HAMR). HAMR may also sometimes be referred to as thermally assisted magnetic recording (TAMR) or optically assisted magnetic recording (OAMR).
Conventional HAMR media is typically composed of a substrate, a heat sink layer, seed and nucleation layers, and a magnetic recording layer. Desirable properties of the magnetic recording layer in HAMR media include a moderate Curie temperature and a uniform, well-segregated, high magnetic anisotropy grain structure with highly developed crystallographic texture. Even with a magnetic recording layer that exhibits these properties, HAMR media may still suffer from high DC read back noise level during the read back process. The high DC read back noise level is an intrinsic characteristic of signal-layer HAMR media, and this noise level is expected to increase as the size of the reader element shrinks.
Multi-layer HAMR media structures have been explored and discussed, for example, in U.S. Pat. No. 7,678,476 B2 to Weller et al. (hereinafter “Weller”). In Weller, an HAMR media structure with a capping layer on top of the magnetic recording layer is proposed. The capping layer in Weller has a Curie temperature lower than that of the magnetic recording layer. The purpose of this capping layer in Weller is to provide magnetic stabilization to the lower magnetic recording layer at storage temperatures. This capping layer in Weller, however, does not address the high DC read back noise level during read back of the media.